Here's a theoretically simple, cut-and-jump mod for the existing
Black Cat Systems 22 meter Beacon Kit. The mod provides operation on a different frequency than originally intended: in the frequency range anywhere from about 80 meters to 40 meters.
Note: This is not an official authorized mod. Black Cat Systems had nothing to do with this mod.
Build and test your original kit first the way it was originally designed.
Then if you choose to do this mod, do it while knowing that it started out working OK.
If you mess up your kit, don't blame Black Cat Systems.
When you do this kind of crazy mod, it is
totally your own responsibility.
Hams can use this mod for a ham band beacon
With the warnings having been duly admonished, onward to the actual beacon mod:
The oscillator.
It's hard to beat a cheap programmable clock oscillator for simplicity of frequency choice.
Fixed-frequency clock oscillators can also be utilized for this purpose.
A programmable oscillator can be ordered from Digikey or another electronics dealer, pre-programmed to any frequency, or a
programmer system can be acquired and you can program it yourself.
Theory of the mod circuit:
- The programmable oscillator is keyed by the microprocessor's keying line, via one inverter of the 74HC02 that had originally been utilized as the crystal oscillator. Since the microprocessor asserts a logic Low on the keying control line for "transmit", the keying line needs to be inverted to key the programmable oscillator's control input (which requires logic Hi for operation).
- The programmable oscillator (see data sheet) pulls as much 45mA., so power consumption can be reduced by keying the entire oscillator on/off.
- The oscillator output feeds into the remaining 3 inverter sections of the 74HCO2, which act as as a power amplifier, as originally designed.
- The Power Amplifier feeds the Low Pass Filter (LPF) which is modded with capacitors and inductors to reduce harmonic energy, with a cut-off just above 7 MHz.
- The Low Pass Filter output feeds the antenna or dummy load.
Theoretical procedure:
1. Remove Y1 crystal.
2. Remove capacitors C4, C16, C17, C18.
3. Remove Jumper at C16.
4. Remove RV1 and put a jumper on the bottom of the PCB in place of it for full power.
5. Do the other cut-and-jump mods around the 74HC02.
6. Remove the L1, L2, toroid inductors and replace with the 2 new leaded 1.5uH inductors in the Low Pass Filter mod.
7. Add the 3 capacitors C3, C8, C9, in the Low Pass Filter mod and leave all the original capacitors in place.
8. Double sticky foam tape the Programmable Oscillator upside down (dead bug style) to the board in the area where the crystal was.
9. Wire the Programmable Oscillator into the appropriate points on the board.
10. Test the unit on a dummy load or ~50 ohm resistor.
Theoretical Parts List for mod version 1d.
QTY, Description,
Value2pc, Inductor, 1.5uH
part link Digikey2pc, Capacitor, 470pF
part link Digikey1pc, Capacitor, 680pF
part link Digikey1pc, Programmable Oscillator, CPPC4-HT5RT
part link Digikey Below:
Schematic of theoretical mod version 1d.
Below: Large size schematic of theoretical mod version 1d.
You own it, it is yours to break.
Topic: Mod Black Cat Beacon Kit (Read 2853 times)
